When it came to dealing with positive and negative skills, the biggest problem was striking a fine balance. The power of the Xuan Yellow Sutra and Blood-Pulse Sutra had to be perfectly balanced if they were to be merged. That was integral.
In the universe of kingdoms, Han Sen was unable to use the Blood-Pulse Sutra's power unless he broke the rules of suppression that dictated the world. Breaking the rules was the only way he could use of Blood-Pulse Sutra.
Even so, in a situation in which one power received support from the rules of the world and the other was repelled by the powers of the world, wanting to strike a perfect balance between the two powers was extraordinarily difficult.
Because of God's warning, Han Sen did not want to destroy the rules of the world. That had become obvious. Thus, his careful practice wasn't yielding many results.